When smart-phones came in the market, mainly when the “iPhone” was first launched, real always-on service was used for the first time in cellular networks. This has created a number of issues. First, many always-on applications generate frequent traffic, e.g. for keep alive messages and status updates, which bring significant problems. Second, the signaling in the network increases a lot due to frequency context establishment and release, e.g. for RRC Connected—RRC IDLE transition. In many networks, this becomes a severe dimensioning problem for the whole network. Third, the UEs battery life is short. Fourth, for devices that generate always-on sparse traffic, the overhead is very large related to the data payload transmission.
In 3GPP LTE/LTE-A systems, DRX mechanism is adopted to support sleep mode while there is no data transmission during RRC Connected state. It is observed that DRX might have a trade-off between data latency and UE power consumption. For example, using long DRX may have low power consumption but increase the latency. In addition, services in smart-phones may be categorized into background traffic and interactive traffic that would have respective requirements. As a result, switching on the DRX configurations for different traffic is expected to be beneficial. To support the feature, UE needs to indicate its performance preference (depended on its running applications, user behavior, and hardware operations) to eNB for configuring DRX appropriately.
Until now, 3GPP has agreed to introduce signaling from the UE to the network that allows the UE to toggle between a “default” state and a “lower power consumption” state, where it is up to the network on whether and how to make use of the preference indication from the UE. For UE preference reporting, the main problem may be excessive reporting when UE wants a fast adapting DRX. Since the decisions and configurations of DRX is controlled by eNB and the DRX state-switching aspect may be different from UE and eNB point of view, eNB needs a control mechanism to avoid frequent reporting. In addition, due to UE mobility, eNB needs to specify whether the preference reporting shall be reported again after HO or eNB shall negotiate on the information.
Besides power saving preference, another useful information is speed information. For UE speed information, how to represent the information to eNB is the problem. Although an accurate value (e.g., physical speed) could provide more information, it also increases the reporting overhead and demands more sophisticated algorithm at the network side. How useful is the speed information really depends on the network algorithm, which decides the speed information shall be provided in certain representation (e.g. granularity, etc.). In addition, mechanisms are also needed to control excessive reporting to reduce signaling overhead.
One objective for UE to report speed information is to assist eNB to decide whether it is better to keep the UE in RRC Connected longer or release the UE to RRC IDLE shortly after buffer becomes empty. In other words, to assist eNB to decide the length of the RRC inactivity timer that is used to control how long the UE will be released to RRC IDLE after the belonged buffer is empty. With speed information, eNB could consequently apply proper RRC inactivity timer for the UE and save the signaling overhead due to the avoidance of frequent handover by releasing UE to IDLE. That is, the UE will perform cell reselection instead of handover to deal with its mobility and that cell reselection does not introduce any signaling. Such signaling overhead is apparently related to UE speed. However, if UE only reports its mobility state, eNB might not be able to decide a proper RRC inactivity timer since it has no clue on the history of state transition of the UE. For example, when a UE report its speed is high, the eNB might release it to IDLE quickly after empty buffer (HO signaling is more than cell reselection). However, if the UE has history of frequent transition, a better decision is to keep the UE in connected mode (HO signaling is less than RRC connection establishment signaling). Therefore, it is insufficient to decide the RRC inactivity timer based on speed information only.
A solution is sought.